Conventionally, a chlorine-containing bleaching agent such as sodium hypochlorite or sodium chlorite is often used for a bleaching treatment for bleaching a fiber product. However, the bleaching treatment using the chlorine-containing agent requires a strict monitoring system and a treatment facility with the possibility that a treatment liquid containing a highly toxic chlorine compound is drained. This disadvantageously leads to higher costs.
Lately, a more environmentally-friendly bleaching treatment is often performed by using hydrogen peroxide instead of the chlorine-containing bleaching agent. If metal ions are present, however, hydrogen peroxide is decomposed due to the catalytic action of the metal ions, resulting in embrittlement of the fiber product. This disadvantageously impairs the texture of the fiber product. These conventional bleaching treatments are each performed by immersing the fiber product in a treatment liquid containing not only the bleaching agent but also a refining agent at a higher temperature, for example, on the order of 80° C. to 120° C. for a long period of time, thereby requiring significantly higher costs for chemical agents and energy. Further, these bleaching treatments are ecologically problematic.
On the other hand, novel bleaching methods employing ozone (O3) are proposed, some of which have been put into practical use (see Patent Documents 1 to 3).    Patent Document 1: JP-A-HEI9 (1997)-31840    Patent Document 2: JP-A-2001-164458    Patent Document 3: JP-A-HEI7 (1995)-11565